diff --git a/core/wasm_shims/cnc_sim_wasm_runtime_probe_main.cc b/core/wasm_shims/cnc_sim_wasm_runtime_probe_main.cc
index 6aa9b65..8fdf44c 100644
--- a/core/wasm_shims/cnc_sim_wasm_runtime_probe_main.cc
+++ b/core/wasm_shims/cnc_sim_wasm_runtime_probe_main.cc
@@ -1,4 +1,5 @@
 #include "cnc_sim_api.h"
+#include "boost/python/object.hpp"
 #include "hal.h"
 #include "libnml/nml/stat_msg.hh"
 
@@ -9,6 +10,14 @@
 #include <vector>
 #include <wordexp.h>
 
+extern int _task;
+
+extern "C" {
+extern PyObject *PyInit_interpreter(void);
+extern PyObject *PyInit_emccanon(void);
+extern struct _inittab builtin_modules[];
+}
+
 // LinuxCNC source basis: src/emc/rs274ngc/rs274ngc_pre.cc provides read(),
 // execute(), and wordexp() paths; interp_convert.cc converts G0, G2, and M30.
 // src/emc/rs274ngc/interp_namedparams.cc calls the HAL lookup functions
@@ -129,6 +138,23 @@ bool nml_status_constructors_match_linuxcnc() {
            status._state == -1;
 }
 
+bool builtin_modules_match_linuxcnc_preview_runtime() {
+    // LinuxCNC source basis: src/emc/rs274ngc/gcodemodule.cc defines _task=0
+    // for preview and registers interpreter/emccanon builtin module entries;
+    // src/emc/task/taskclass.cc uses the same builtin module table shape.
+    return _task == 0 &&
+           builtin_modules[0].name &&
+           std::strcmp(builtin_modules[0].name, "interpreter") == 0 &&
+           builtin_modules[0].initfunc == PyInit_interpreter &&
+           builtin_modules[0].initfunc() == nullptr &&
+           builtin_modules[1].name &&
+           std::strcmp(builtin_modules[1].name, "emccanon") == 0 &&
+           builtin_modules[1].initfunc == PyInit_emccanon &&
+           builtin_modules[1].initfunc() == nullptr &&
+           builtin_modules[2].name == nullptr &&
+           builtin_modules[2].initfunc == nullptr;
+}
+
 } // namespace
 
 int main() {
@@ -147,6 +173,9 @@ int main() {
     if (!nml_status_constructors_match_linuxcnc()) {
         return 9;
     }
+    if (!builtin_modules_match_linuxcnc_preview_runtime()) {
+        return 10;
+    }
 
     std::vector<CncSimEvent> events;
     CncSimHandle *sim = cnc_sim_create();